Variable displacement pumps have previously been described. These pumps usually comprise a pump housing with a pump rotor, whereby the pump rotor is provided with radially slidable vanes rotating in a shiftable control ring. The control ring is pushed into a low or a high pumping volume direction depending on the rotational speed of the engine. If the rotational speed increases, the control ring is pushed into a low pumping volume direction; if the rotational speed decreases, the control ring is pushed into a high pumping volume direction so that the lubricant can be pressurized at a more or less constant level, independent of the rotational speed of the pump rotor or engine.
The lubricant pressure requirement is, however, dependent on the working conditions of the engine. The lubricant pressure requirement is lower at low rotational speeds and higher at high rotational speeds of the engine. A device with a control system which provides one level of pressure of the pressurized lubricant is described in WO 2005/026553 A1.